linux-kernel - Re: [PATCH] virtio_net: enable big packets for large MTU values

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Message-ID: <20170329191324-mutt-send-email-mst@kernel.org>
Date:   Wed, 29 Mar 2017 19:13:33 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH] virtio_net: enable big packets for large MTU values

On Wed, Mar 29, 2017 at 03:38:09PM +0300, Michael S. Tsirkin wrote:
> If one enables e.g. jumbo frames without mergeable
> buffers, packets won't fit in 1500 byte buffers
> we use. Switch to big packet mode instead.
> TODO: make sizing more exact, possibly extend small
> packet mode to use larger pages.
> 
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>

Fixes: 14de9d114a82 ("virtio-net: Add initial MTU advice feature")

> ---
>  drivers/net/virtio_net.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index e0fb3707..9dc31dc 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2428,6 +2428,10 @@ static int virtnet_probe(struct virtio_device *vdev)
>  			dev->mtu = mtu;
>  			dev->max_mtu = mtu;
>  		}
> +
> +		/* TODO: size buffers correctly in this case. */
> +		if (dev->mtu > ETH_DATA_LEN)
> +			vi->big_packets = true;
>  	}
>  
>  	if (vi->any_header_sg)
> -- 
> MST